Project Summary Glioblastoma multiforme (GBM) accounts for 46% of all brain tumor malignancies and result in a poor prognosis and median survival of only a few months. Despite our current knowledge on mechanisms driving glioma stem cells to promote malignant phenotypes of GBM and current treatment modalities, there still remains a significant problem with poor overall survival for patients suffering with GBM. Therefore, it is imperative that we gain new insights into the biology of GBM and glioma stem cells to develop more effective targeted therapies. The goal of this project is to gain further understanding of mechanisms driving glioma stem cells facilitated by the truncated glioma-associated oncogene homolog 1 (tGLI1) transcription factor discovered in our lab. We have shown that tGLI1 expression is tumor specific and that it is a gain-of-function GLI1 transcription factor, which is the nuclear effector of the hedgehog (Hh) signaling pathway. The Hh pathway is important for stem cell self-renewal and is aberrantly active in many cancers including GBM. We have also shown that tGLI1 increases angiogenesis, migration, and invasiveness of GBM in a subcutaneous xenograft model. The effect of tGLI1 on glioma stem cells has never been studied. Our preliminary results show that tGLI1 is highly expressed in patient GBM samples, correlates with poor overall survival, and is enriched in the mesenchymal subtype of GBM. Preliminary studies also revealed that tGLI1 is upregulated in GBM stem cells and promotes formation and growth of neurospheres. Furthermore, our preliminary data shows that tGLI1 promotes growth of GBM in an orthotopic mouse model. Based on the above-mentioned rationale, we hypothesize that the novel tGLI1 transcription factor regulates glioma stem cell self-renewal and proliferation, thereby promoting malignant phenotypes of GBM. To test our hypothesis we will determine the role of tGLI1 in glioma stem cells in vitro (Aim 1) and examine whether tGLI1 promotes glioma stem cell growth in vivo (Aim 2). Our project could define tGLI1 as a novel mediator of glioma stem cells and gliomagenesis and establish tGLI1 as a prognostic indicator for aggressive GBM.